This research will examine the interactions between outgrowing neurons and their embryonic environment that enable their precise navigation through the embryo to their target cells. We will focus on the role of extracellular matrix in the form of basal lamina as a substratum for neuron outgrowth. Neuronal interactions with the basal lamina will be examined in the peripheral nervous system of the grasshopper embryo whose simple organization and experimental suitability permit both a detailed description of neuron-substratum interactions at the cellular and molecular levels, and experimental testing of hypotheses. We will examine the distribution of different basal lamina components and their relationship to growing neurons, by light and electron microscopy using monoclonal antibodies prepared to basal lamina. We will determine the biochemical nature of basal lamina components using a variety of biochemical techniques on material isolated by immunoprecipitation or affinity chromatography. We will test the role of these components in guiding axon outgrowth in experiments in which embryos are cultured in the presence of antibodies or biochemical reagents affecting specific basal lamina components, or in which individual neurons are cultured on different basal lamina substrata, and the resulting neuronal pathways evaluated. The results of these experiments will increase our understanding of axonal guidance during nervous system development in general and may allow us to develop principles and tests that can be used to study more complex nervous systems not currently amenable to this level of analysis.